Sync ics url calendar

[ellypsis]

## Enhancement ##
Add the possibility to sync from an url which point to an ics calendar.
For exemple : facebook (I know, shame on me...)

[hummlbach]

Yes, shame on you! added ellypsis to the ignore list ;-)
But as facebook isn't the only source of ics files, i think we can except this enhancement. :-)
@mardy how would we do something like that?

[ellypsis]

I know that vdirsyncer can source ics files. It is used as sync service for application on linux environment.
vdirsyncer GitHub
I try to use it as workaround to sync ics file with one of my caldav calendar.